.\" -*- nroff -*-
.\" Copyright (c) 2012      Oracle and/or its affiliates.  All rights reserved.
.\" Copyright 2012 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Improbe 3 "Jun 10, 2020" "4.0.4" "Open MPI"
.SH NAME
\fBMPI_Improbe\fP \- Non-blocking matched probe for a message.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Improbe(int \fIsource\fP, int\fI tag\fP, MPI_Comm\fI comm\fP,
	int\fI *flag\fP, MPI_Message\fI *message\fP, MPI_Status\fI *status\fP)

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
source
Source rank or MPI_ANY_SOURCE (integer).
.TP 1i
tag
Tag value or MPI_ANY_TAG (integer).
.TP 1i
comm
Communicator (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
flag
Flag (logical).
.ft R
.TP 1i
message
Message (handle).
.ft R
.TP 1i
status
Status object (status).
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
Like MPI_Probe and MPI_Iprobe, the MPI_Mprobe and MPI_Improbe operations
allow incoming messages to be queried without actually receiving
them, except that MPI_Mprobe and MPI_Improbe provide a mechanism to
receive the specific message that was matched regardless of other
intervening probe or receive operations.  This gives the application
an opportunity to decide how to receive the message, based on the
information returned by the probe.  In particular, the application may
allocate memory for the receive buffer according to the length of the
probed message.
.sp
A matching probe with MPI_PROC_NULL as \fIsource\fP returns \fIflag\fP
= true, \fImessage\fP = MPI_MESSAGE_NO_PROC, and the \fIstatus\fP object
returns source = MPI_PROC_NULL, tag = MPI_ANY_TAG, and count = 0.
.sp
MPI_Iprobe returns a true value in \fIflag\fP if a message has been
matched and can be received by passing the \fImessage\fP handle to the
MPI_Mrecv or MPI_Imrecv functions, provided the \fIsource\fP was not
MPI_PROC_NULL.

.SH NOTE
This is an MPI-3 function and has no C++ binding.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument. C++
functions do not return errors.
.sp
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
MPI_Comm_set_errhandler; the predefined error handler
MPI_ERRORS_RETURN may be used to cause error values to be
returned. Note that MPI does not guarantee that an MPI program can
continue past an error.

.SH SEE ALSO
.ft R
.nf
MPI_Mprobe
MPI_Probe
MPI_Iprobe
MPI_Mrecv
MPI_Imrecv
MPI_Cancel
